Scientists Say New Strain of Swine Flu Virus Is Spreading to Humans in China

HONG KONG — A new strain of the H1N1 swine flu virus is spreading silently in workers on pig farms in China and should be “urgently” controlled to avoid another pandemic, a team of scientists says in a new study.

H1N1 is highly transmissible and spread around the world in 2009, killing about 285,000 people and morphing into seasonal flu.

The newer strain, known as G4 EA H1N1, has been common on China’s pig farms since 2016 and replicates efficiently in human airways, according to the study published on Monday. So far, it has infected some people without causing disease, but health experts fear that could change without warning.

“G4 viruses have all the essential hallmarks of a candidate pandemic virus,” the study said, adding that controlling the spread in pigs and closely monitoring human populations “should be urgently implemented.”

The study, published online in the journal Proceedings of the National Academy of Sciences, is based on the surveillance of pigs in 10 Chinese provinces from 2011 to 2018. In the last three years of the study, researchers collected 338 blood samples from workers on 15 pig farms and 230 from people in nearby households.

The study found that 10.4 percent of the workers and 4.4 percent of the others tested positive for antibodies to G4 EA H1N1, and that workers between the ages of 18 and 35 tested positive at a higher rate: 20.5 percent.

Predicting risk is not a precise science, but close attention to the virus would be advisable, said Ian H. Brown, the head of the virology department at Britain’s Animal and Plant Health Agency and one of two scientists who reviewed the paper before it was published.

“It may be that with further change in the virus it could become more aggressive in people much as SARS-CoV-2 has done,” Dr. Brown said in an email on Tuesday, referring to the new coronavirus.